1. Field of the Invention
The invention relates to a device for the back rounding of book blocks in a bookbinding machine with a conveyor device for the book blocks and with rounding elements which are driven in rotation by a driving arrangement. More particularly, the invention relates to a device for the back rounding of book blocks which, after taking up the book block and following its release by the conveyor device, act on both sides of the book block through a defined rolling movement and through pressure.
2. Description of Related Art
In industrial book production the back and, at the same time, the front edge of the book block undergo a change in shape in the back rounding process section. This is primarily performed by means of the roller rounding principle in book block processing machines. In this case a smooth relative displacement of the individual leaves or printed sheets takes place through rounding rollers rolling on the book block sides over a defined rotational angle while pressure is simultaneously applied, the leaves or printed sheets being increasingly pushed towards the book block center as the book block passes through the rounding rollers.
The rounding operation forms the book block back as a circular arc or a flattened arc, which is crucial for the subsequent process section of backing the book block back with regard to the desired back profile of the book block.
When employing the back rounding principle through rounding rollers, the shape of the back is influenced by various factors, such as contact force of the rounding rollers, rotational angle of the rounding rollers, and by the diameter of the rounding rollers.
In the backing process section the rounded book block is finally given the desired back shape, which is in accordance with the binding method and is determined by a fold which is provided in the region of the book block near the back and which may be formed either as a deep fold with an angle of up to 90.degree. or as a shallow or oblique fold with an angle of up to 45.degree.. The backing is carried out by a formed piece reciprocating over the entire width of the back, whereby pressure and friction are applied to bend over the folded printed sheets from the center of the book block back to both sides at an angle which increases towards the outside. The book block is thus given its mushroom-like back shape while being stabilized at the same time. In order to carry out the backing operation, the book block is gripped between backing boards with a defined projecting length from the rounding end.
A book rounding and backing machine with rounding rollers rolling on both sides of the book block and with a formed piece acting on the book block back is represented and described as an example in DE-OS 15 36 507.
The folded width between the folded edge and the rounding end is to be adjusted according to the folded forms, this taking place through vertical adjustment of the book block between the backing boards, i.e., through varying the length projecting from the backing boards.
A bookbinding machine for the back rounding of book blocks with rounding rollers which can travel vertically in recesses in a clamping jaw is known from the European Patent Specification 0 444 409 assigned to the assignee hereof. The vertical movement of the rounding rollers is superimposed on the rotational movement so as to compensate for the vertical movement of the book block produced due to the rotational movement. The outer leaves of the book block are held at a constant level. The rounding rollers are located at pivot levers which can travel vertically and move at the sides of the book block, and the rotational movement of the rounding rollers is derived from the vertical movement. The rounding rollers are driven in rotation by the driving arrangement of the pivot levers as a result of a gearwheel of the driving arrangement rolling on a stationary rack through a vertical movement of the pivot levers.